The new Wembley Stadium was evacuated and workers sent home today after an incident involving a roof, the GMB union said.

Union officials said workers heard "an enormous bang" and it was later discovered a rafter in the roof had failed.

No one is believed to have been hurt in the incident but union officials will launch a full investigation into what happened.

A spokesman for construction company Multiplex said: "Between 8.30am and 8.50am there was a full evacuation of the site. 3,000 people were removed.

"Something happened with the roof above certain workers. It was a rafter in the roof that failed while it was being welded. It fell three feet. No one was injured.

"It was an isolated incident. Standard procedures were used to withdraw people from the situation. Engineers are looking at it now."

The GMB union said most workers on the Wembley site had been sent home for the day following the incident.

Earlier this month, it was announced that the FA Cup Final would be played in Cardiff after Multiplex could not guarantee that the £757 million 90,000-seater stadium would be ready for May 13th.

The FA had already allowed Multiplex to move the completion deadline several times. The original autumn 2005 handover date was pushed back to January 31st 2006 and then March 31st.

Multiplex is expected to lose more than £100million on building the stadium and it is understood the Australian company will be penalised £1million a week for over-running the deadline.

PA